Specific binding site

Affinity chromatography is used in the preparation of more highly purified Factor IX concentrates (53—55) as well as in the preparation of products such as antithrombin III [9000-94-6] (56,57). Heparin [9005-49-6], a sulfated polysaccharide (58), is the ligand used most commonly in these appHcations because it possesses specific binding sites for a number of plasma proteins (59,60). 

CREB stands for cyclic-AMP response element (CRE) binding protein and is a transcription factor. When phosphorylated by cyclic AMP- and cyclic GMP-dependent Protein Kinases or other protein kinases it binds to gene promoters that contain a specific binding site. After binding, the respective transcription activity is modulated. 

The contractile apparatus may be thought of as the sum of those intracellular components which constitute the machinery of chemomechanical transduction. It is the set of proteins which convert the chemical energy of the terminal phosphate ester bond of ATP into mechanical work. The structure of the contractile apparatus is determined by the connections between the various protein molecules via specific binding sites or, in a minority of cases, via labile covalent linkages. The kinetics of the contractile machinery are determined by the regulation of changes in these connections. 

In general, the receptor-G-proteins complexes exchange bound GDP for GTP. In turn, the two, smaller subunits of the G-protein components of these complexes are released and the receptor protein dissociates. The remaining G-protein GTP complex then complexes with and activates a specific enzyme. It is very significant to note that G-proteins therefore have at least three specific binding sites (a) for nucleotides, (b) for a receptor protein, and (c) an effector protein. 

Mutations in bacteria and mammalian cells (including some that result in human disease) have supported these conclusions. Facilitated diffusion and active transport resemble a substrate-enzyme reaction except that no covalent interaction occurs. These points of resemblance are as follows (1) There is a specific binding site for the solute. (2) The carrier is saturable, so it has a maximum rate of transport (V Figure 41-11). (3) There is a binding constant (Al) ) for the solute, and... 

Huang et al. (7) suggested that the brevetoxin binding site lies in the hydro-phobic portion of the channel, and since PbTx-1 and PbTx-7 are also the most hydrophobic of the toxins, their potency may also be in part due to solubility considerations. In general, the more hydrophobic the toxin, the higher is its potency and ability to displace tritiated PbTx-3 from its specific binding site. It is our contention that substituent character on each toxin s K (type-1) or J (type-2) ring... 

Complex formation among the three protein components of the M. trichosporium OB3b MMO has been demonstrated (66). In this work, it was hypothesized that protein B binds tightly to Hox to form an activated complex but that, after formation of H, the binding affinity is diminished (63, 66). Results reported for M. capsulatus (Bath) are consistent with initial binding of Hox to protein B to form an activated complex (51), because increased yields and rate constants are seen when protein B is added to Hred. If the Hred-protein B complex of M. capsulatus (Bath) is the species influencing reactivity, then there should be a direct relationship between equivalents of added B and the rate constant, at which point the B-specific binding sites would be saturated. Since H is a dimer two equivalents of protein B... 

Phencyclidine (1 -[1-phenylcyclohexyl]pi peridine HC1 PCP) and its active derivatives produce unique behavioral effects in animals and psychotomimetic effects in humans. Drugs of this class have been demonstrated to bind saturably, reversibly, and with high affinity to specific binding sites in brain (Hampton et al. 1982 Quirion et al. 1981 Sircar and Zukin 1983 Vincent et al. 1979 Zukin and Zukin 1979). These sites have been shown to exhibit a characteristic heterogeneous regional distribution pattern (Quirion et al. 1981 Sircar et al., submitted for publication Zukin and Zukin 1979) distinct from that of any other receptor type. 

Beside a crystal cavity of suitable size, additional information is required, e.g. designed polarity gradients in the cavity or carefully located and specific binding sites, respectively. At best, the crystal inclusion will enjoy an ideal lock and key relation 23 between host and guest components from a chemical and spatial point of view. 

In the process of mediated transport, carrier proteins embedded within the plasma membrane assist in the transport of larger polar molecules into or out of the cell. When a given substance attaches to a specific binding site on the carrier protein, the protein undergoes a conformational change such that this site with the bound substance moves from one side of the plasma membrane to the other. The substance is then released. Mediated transport displays three important characteristics influencing its function ... 

An ionophore is a compound that is capable of selectively carrying ions across a membrane. The ion fits into a specific binding site in a molecule that is hydrophobic enough to cross the membrane. There are calcium-specific ionophores, proton ionophores, sodium ionophores, etc. 

TABLE 1. Main characteristics of 3H-LSD- and 3H-PCP-specific binding sites in the rat brain... 

The three regions indicated for each ligand correspond to those containing the highest densities of related specific binding sites. 

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